This invention relates to a safety winch of a type particularly, but not exclusively designed for paying out and reeling in a cable attached to a person when entering a hazardous zone so the person can be extracted by the winch if necessary.
It is well known that persons entering hazardous situations such as underground pipelines, storage containers and the like can encounter difficulties such as poisonous fumes which can place the person in difficulty or even causing unconsciousness. In such a situation it is necessary for the person to be extracted from the danger without the necessity of a second person entering the same zone and possibly befalling the same fate.
As safety consciousness has developed, therefore, it has been necessary to attach to persons entering such a zone a cable attached to a harness worn by the person with the cable extending to a suitable hoist system which allows the cable to be reeled in and the person extracted from the dangerous situation. Many winches are available which provide sufficient power to allow the person to be extracted including lifting the person vertically, should this be necessary. Hand winches of this type are available which can develop sufficient force from hand operation to withdraw the person. These winches generally include a brake mechanism so that the cable is prevented from being rapidly paid out should the winch be inadvertently released, for example when lifting the person from an underground location. It will of course be appreciated that, should the winch be released or the brake fail, the person can be dropped with the possibility of causing injuries beyond those already sustained.
Conventional winches are therefore unsatisfactory as they do not provide sufficient fail safe operation and such they do not have the flexibility of drive arrangements to enable the winch to be operated in a manner which avoids interfering with the normal operation of the person while in the dangerous location but yet provides the ability to extract the person and to generate sufficient power to ensure that the person can be properly lifted.
According to the a first aspect of the invention there is provided a safety winch comprising a main frame, a cable, a main axle, a secondary axle, means mounting the main axle and the secondary axle on the main frame each for rotation about a respective one of two parallel axles, a drum mounted on the main axle for rotation therewith in a first direction to cause pay-out of said cable and in a second direction to cause reel in of said cable, chain drive means for communicating rotation of each of the main axle and the secondary axle to the other of the main axle and the secondary axle, handle means for manually driving the secondary axle, and a safety brake arrangement operable to prevent rotation of the main axle in said first direction, the safety brake arrangement comprising first safety brake means mounted on the main axle and second safety brake means mounted on the secondary axle, each of the first and second safety brake means being arranged to allow rotation of the main axle in said second direction to cause reel in of the cable and being arranged to prevent rotation of the main axle in said first direction except when the main axle is driven from said chain drive means in said first direction.
According to a second aspect of the invention there is provided a safety winch comprising a main frame, a cable, a main axle, a secondary axle, means mounting the main axle and the secondary axle on the main frame each for rotation about a respective one of two parallel axes, a drum mounted on the main axle for rotation therewith in a first direction to cause payout of said cable and in a second direction to cause reel in of said cable, chain drive means for communicating rotation of each of the main axle and the secondary axle to the other of the main axle and the secondary axle, handle means for manually driving the secondary axle, and a safety brake arrangement operable to prevent rotation of the main axle in said first direction, said safety brake assembly comprising a ratchet wheel mounted on the main axle for rotation about the axis of the main axle relative to the main axle, a pawl mounted on the frame and cooperating with the ratchet wheel to prevent rotation thereof in said first direction, a drive member receiving drive from said chain drive means and mounted on the main axle for rotation about the axis of the main axle, friction pad means between the drive member and the ratchet wheel and cam means between the main axle and the drive member allowing limited rotational movement between the main axle and the drive member and operable in said second direction of movement of the drive member to cause the friction pad means to form a frictional connection between the drive member and the ratchet wheel to communicate drive from the drive member to the ratchet wheel and operable in said first direction of movement of the drive member to move the friction pad means axially to separate said frictional connection to allow rotation of the drive member and the main axle relative to the ratchet wheel.
According to the third aspect of the invention, there is provided a safety winch comprising a main frame, a cable, a main axle, a secondary axle, means mounting the main axle and the secondary axle on the main frame each for rotation about a respective one of two parallel axes, a drum mounted on the main axle for rotation therewith in a first direction to cause payout of said cable and in a second direction to cause reel in of said cable, chain drive means for communicating rotation of each of the main axle and the secondary axle to the other of the main axle and the secondary axle, handle means for manually driving the secondary axle, and a safety brake arrangement operable to prevent rotation of the main axle in the said first direction, a first sprocket mounted on the secondary axle at an end thereof opposite to said chain drive means, a drive sprocket mounted on said main frame, a chain communicating drive from the drive sprocket to the first sprocket, each of said first sprocket and said drive sprocket having means thereon for engagement with said handle means for communication of manual drive thereto from said handle means, the drive sprocket and the first sprocket being arranged such that a drive ratio between the drive sprocket and the main axle is different from a drive ratio between the first sprocket and the main axle.
One embodiment of the invention will now be described in conjunction with the accompanying drawings in which: